Randomness and Similarity of Concrete Permeability in a Natural Tidal Environment

This work first analyzes the time-dependent property of average concrete permeability by the relative decline ratio and proposes an analysis method for the randomness of time-dependent variables. Then, based on exposure test results of 10 different concretes in a natural tidal environment, the average time-dependent processes, statistical parameters, and probability distributions of the instantaneous chloride diffusion coefficient ($D_{\mathrm{ins}}$), water permeability coefficient ($K_w$), and intrinsic gas permeability coefficient ($K_g$) were all studied. Similarities among the randomness of three concrete permeabilities were analyzed by the Kullback-Leibler (K-L) divergence. Results indicate that decreasing processes of three permeability coefficients with increasing exposure time show similarities. The decreases are all faster at the early exposure stage and gradually stabilize at the later stage. Specifically, the decline rate of average $K_w$ is the greatest, followed by that of $K_g$, and the decline rate of $D_{\mathrm{ins}}$ is the smallest. When ignoring the influence of material components, generally, both $D_{\mathrm{ins}}$ and $K_w$ follow a normal distribution, and $K_g$ follows a lognormal distribution. The randomness of $K_w$ is the greatest, and that of $D_{\mathrm{ins}}$ is the smallest. The randomness of both $K_w$ and chloride diffusion coefficient of concrete without admixture are both greater than those of concrete with admixture. The randomness of intrinsic gas permeability of concrete with admixture is greater than that of concrete without admixture. Results show good similarities among the three permeability coefficients of concrete, and $D_{\mathrm{ins}}$ is more similar with $K_w$ in random characteristics. Similarities among the randomness of three permeabilities in concrete without admixture are more obvious than those of concrete with admixture.